Power-based hardware diversity

ABSTRACT

A power-based hardware antenna diversity method for a wireless transceiver with multiple antennas is disclosed. The method is characterized in the steps of setting the transceiver gain at a maximum level to establish a first story of dynamic power range above a noise floor level, using a high-resolution ADC at a large back-off level relative to the noise floor to detect weak signals within the first story of the dynamic power range, switching antennas and measuring power level for each antenna during signal onset, and selecting an antenna having a largest power level.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to provisional application No.60/496,734, entitled “Power-Based Hardware Diversity” filed on Aug. 21,2003, which is herein incorporated by reference for all intents andpurposes related.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communications, and moreparticularly to a packet-by-packet power based hardware diversity schemefor selecting one of multiple antennas to reduce the probability of poorreception and improve reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The benefits, features, and advantages of the present invention willbecome better understood with regard to the following description, andaccompanying drawings where:

FIG. 1 is a simplified block diagram of a wireless transceiverimplemented according to an exemplary embodiment of the presentinvention;

FIG. 2 is a figurative diagram of a portion of an OFDM packet symbolstructure with a preamble as provided in the IEEE 802.11a standard;

FIG. 3 a figurative diagram illustrating exemplary division of thedynamic power range or spectrum of the transceiver of FIG. 1;

FIG. 4 is a figurative diagram of an exemplary timeline illustratingantenna measurement and selection within the SS section of an incomingpacket for two antennas; and

FIG. 5 is a figurative diagram of an exemplary timeline illustratingantenna measurement and selection within the SS section of an incomingpacket for 3 antennas.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following description is presented to enable one of ordinary skillin the art to make and use the present invention as provided within thecontext of a particular application and its requirements. Variousmodifications to the preferred embodiment will, however, be apparent toone skilled in the art, and the general principles defined herein may beapplied to other embodiments. Therefore, the present invention is notintended to be limited to the particular embodiments shown and describedherein, but is to be accorded the widest scope consistent with theprinciples and novel features herein disclosed.

Antenna diversity provides increased reliability to a communication linkfor transceivers with multiple antennas in which each antenna “sees”different channels. Diversity reduces the probability of poor receptionby instantaneously selecting the best antenna for each packet. Two typesof antenna diversity are known, including those based in firmware andthose based in hardware. Firmware diversity may be implemented in themedia access controller (MAC) in which the antenna is selected accordingto some algorithm implemented in firmware based on a packet errormetric, such as packet error rate (PER) or the like. Firmware diversitymethods are relatively slow and are effective for relatively simple andstatic environments. For example, the antenna decision is not made on apacket-by-packet basis but is instead made on a cumulative packet metricover multiple packets, such as when the PER becomes unacceptable overtime.

Hardware diversity is relatively fast and makes antenna decisions usinghigh-speed hardware techniques. An antenna decision is made everyreceived packet (packet-by-packet) in which two or more antennas areexamined during the front part of the preamble of each packet. Thepreferred antenna is selected for use over the rest of the packet. Theantenna decision is made based on one or more hardware diversitymetrics, including power or the Received Signal Strength Indicator(RSSI), signal-to-noise ratio (SNR), multipath or any suitablecombination thereof. A power- or RSSI-based solution chooses the antennawith best signal strength; an SNR-based solution chooses the antennawith the best SNR; a multipath-based solution chooses the antenna withmost benign multipath characteristic. The noise associated with theSNR-based schemes can be thermal (e.g., radio generated) or caused byinterference, such as by other radio frequency (RF) sources. Thepower-based scheme is generally the same as SNR if the noise is the sameon all antennas.

Utilization of each metric provides some degree of improved reliability.Multipath schemes reduce the amount of “echo” distortion on the signalprovided to the receiver. Power-based schemes increase average powerprovided to the receiver, and are most effective when a communicationlink is SNR-limited (e.g., not multipath limited) and in which the noiseis about the same on all of the antennas. Assume, for example, that areceiver needs approximately 10 decibels (dB) SNR for reliableperformance so that the packet must be at least 10 dB above the noisefloor for reliable detection and reception. If the SNR level of eachantenna is different, then selecting the antenna with the highest SNRincreases the SNR provided to the baseband (BB) processor. Theimprovement in link performance, however, depends upon whether thecommunication link is SNR limited or not. If the link is SNR-limited(e.g., rather than multipath interference limited), then power-basedhardware antenna diversity improves link performance.

The present invention is described in relation to a transceiver 100(FIG. 1) configured in a Zero Intermediate Frequency (ZIF) architecturefor use in a wireless local area network (WLAN) in accordance with anyone or more of the family of IEEE 802.11 standards, such as 802.11a,802.11b, 802.11g, etc. It is understood, however, that the presentinvention is not limited to ZIF architectures or WLAN configurations or802.11 operations, but instead may be employed in other types of radioor wireless communications for other types of applications. A ZIFarchitecture, otherwise known as direct conversion, is a wirelesstransceiver implementation that is utilized to obtain sufficientperformance and higher data throughput at lower cost and powerconsumption by eliminating IF components and external filters. Thetarget carrier frequencies are in the gigahertz (GHz) range, such as forexample, the 2–5 GHz range and higher, although the present invention isnot limited to any particular frequency range.

It is desired to use hardware diversity to make diversity decisions on apacket-by-packet basis using packet preambles since the 802.11 protocolis contention-based in which packets can arrive on a random basis fromany direction at any time. Firmware-based diversity cannot handle thesesituations. Hardware diversity schemes have been designed for single-IF(intermediate frequency) (or non-ZIF) 802.11b radios. Hardware diversityis more difficult to implement, however, for radios that operate athigher data rates and/or that employ the ZIF architecture. There is verylittle time available during the packet preamble of an orthogonalfrequency division multiplexing (OFDM) packet used by transceiversoperating according to the IEEE 802.11a or 802.11g standards as comparedto the time available during the packet preamble of an 802.11b packet.

The time problem is exacerbated when operating with a ZIF architecture,which suffers from excessive DC components. The DC voltage levels canbecome excessively large in the ZIF radio, so that the signals ofinterest become temporarily invisible and difficult to detect andacquire. The primary problem with the ZIF architecture is thedevelopment of DC offsets at baseband that degrade SNR, which isdirectly related to performance of the system. All of the sources of DCoffset may be referenced to the input of the baseband amplifier in thebaseband signal path of the receive signal processing chain. The gainrange of the baseband amplifier must be sufficient to guaranteeacceptable performance in a variety of environments.

The gain range of traditional baseband amplifiers has been configured tooperate at gain levels over 50 dB, for example, which was believednecessary to obtain the desired operating range. It has been determined,however, that at such high gains (50 dB or more), gain changes of aslittle as 10 dB can cause an increase of DC level from essentially 0 to3 V or more. The analog to digital converter (ADC), however, isgenerally limited to a relatively small voltage range (e.g.,approximately 0.5 V), so that excessive DC overwhelms (e.g., saturates)the ADC and causes potential operation failure. For a radio implementedaccording to the IEEE 802.11a standard, for example, the maximum allowedtime to measure and eliminate DC is about 5 to 6 microseconds (μs). TheAGC procedure must be configured to conserve time, which is a valuablecommodity in a wireless transceiver.

The present disclosure describes a packet-by-packet power-based hardwareantenna diversity scheme that is useful for radios implemented using aZIF architecture and that operate according to any of the IEEE 802.11standards, including 802.11a and 802.11g using OFDM. Such WLAN radiostypically have a relatively large dynamic range, such as, for example, adynamic power range from approximately −92 dBm (decibels above or below1 milliwatt) to approximately −10 dBm. It is determined that providing apower-based hardware diversity scheme over the full dynamic power rangeis not necessary. Instead, the full dynamic range is divided into threeranges or power stories for acquisition including a 30 dB range firststory 301 (FIG. 3). During noise floor tracking, the gain is limited toa maximum value and the ADC back-off is large and provides powervisibility within this entire 30 dB range down to the noise floor. Thereis less of a need to switch the antenna if the signal power issignificant (e.g., above the back-off range of the ADC causing ADCclipping).

FIG. 1 is a simplified block diagram of a wireless transceiver 100implemented according to an exemplary embodiment of the presentinvention. The transceiver 100 is configured for dual-band operation inwhich it can operate at 2.4 GHz for 802.11b or 802.11g or 5 GHz for802.11a. The transceiver 100 includes a radio 101, a baseband processor103, and a MAC 105. The radio 101 generally converts between RF andbaseband, and the baseband processor 103 converts between baseband dataand MAC packets provided from, or otherwise for processing by, the MAC105. The transceiver 100 includes at least two antennas, where it isunderstood that any number of antennas is contemplated. The antennas arecoupled to a diversity switch within the radio 101, where the diversityswitch is further coupled to an RX diplexer for receive operations. TheRX diplexer is coupled to a 5 GHz low-noise amplifier (LNA) for 5 GHzoperation according to 802.11a and to a 2.4 GHz LNA for 2.4 GHzoperation according to either 802.11b or 802.11g. The LNAs are bothcoupled to in-phase (I) and quadrature-phase (Q) channel mixers, lowpass filters (LPFs), variable gain amplifiers (VGAs) and correspondingADCs.

The radio 101 further includes a pair of transmit (TX) digital to analogconverters (DACs) respectively coupled to a pair of TX LPFs, which arefurther respectively coupled to a pair of transmitter mixers forup-conversion to RF. The I and Q channel transmit RF signals are eachprovided to a 5 GHz power amplifier (PA) for 802.11a and 802.11g modesand a 2.4 GHz PA for 802.11b mode. The 5 and 2.4 GHz PAs are coupled toa TX diplexer, which is coupled to the antenna diversity switch. Thebaseband processor 103 includes an OFDM processor or kernel for 802.11aor 802.11g operation, an 802.11b kernel, and AGC/DC control logic. Asshown, the baseband processor 103 asserts a hardware diversity controlsignal to the radio 101 for selection of an antenna via the diversityswitch. The diversity control signal directly or indirectly (e.g., via aregister or the like) controls the diversity switch for controllingselection of one of the antennas. Although only two antennas are shown,it is understood that any number of antennas may be employed.

FIG. 2 is a figurative diagram of a portion of an OFDM packet symbolstructure 200 with a preamble as provided in the IEEE 802.11a standard.The standard OFDM packet symbol structure 200 includes a short sync (SS)section 201, followed by a long sync (LS) section 203, followed byremaining packet portions 205 (only partially depicted). The SS section201 includes 10 consecutive short syncs labeled t1, t2, t3, . . . , t10each being 800 nanoseconds (ns) in duration for a total of 8microseconds (μs). The LS section 203 includes a 1.6 μs guard intervalGI2 followed by a pair of 3.2 μs long syncs labeled T1 and T2. Inaccordance with a standard time budget, signal detect, AGC and antennadiversity functions are allotted to occur during the first 7 short syncsor within 5.6 μs of packet onset, which is insufficient time for antennadiversity. The course frequency offset (CFO) estimation and timingsynchronization functions normally occur during the last 3 short syncsbetween 5.6 and 8 μs. The channel and fine frequency offset (FFO)estimation normally occur during the LS section 203.

FIG. 3 a figurative diagram illustrating exemplary division of thedynamic power range or spectrum of the transceiver 100. The dynamicspectrum has a noise floor at approximately −92 dBm, which defines thebottom or floor of a 28 dB first story 301 from −92 dBm to approximately−64 dBm. A 24 dB second story 303 is defined between approximately −64dBm to approximately −40 dBm and a 30 dB third story 305 is definedbetween approximately −40 dBm to approximately −10 dBm. After eachpacket ends, the AGC/DC control circuit of the transceiver 100re-acquires the noise floor and waits for the onset of the next packet.The baseband amplifiers (e.g., including the radio VGAs) are set to amaximum of about 40 dB (assuming the noise floor is within the firststory 301) so that the radio ADCs have an equivalent noise floor valueroughly at about the −92 dBm noise floor level. The ADCs have arelatively large operating range of about 30 dB and thus haveinstantaneous power visibility of the entire power range of the firststory 301. This corresponds to a rather large ADC back-off setting ofthe ADCs of approximately 28 dB spanning the first story 301. A normalback-off level, for example, is about 12 dB, which is otherwisedesirable for lower-resolution ADCs.

The resolution or number of bits of the ADCs depend upon the particularconfiguration and expected signal types to be received. For example, inan 802.11a application, the ADCs are sized to sufficiently distinguish64 quadrature amplitude modulation (QAM) signals which typically requirerelatively large SNR (e.g., such as an SNR greater than 18 dB). In theembodiment shown in which 802.11a and 802.11g signal types arecontemplated, the ADCs includes 8–10 actual bits, although it isappreciated by those of ordinary skill in the art that the “effective”number of bits may be less, such as 7 effective bits or the like.

After acquiring the noise floor, the transceiver 100 measures the powerlevel of the wireless medium over predetermined time intervals, such as,for example, 800 ns time intervals. An increase in power level indicatesthe onset of a packet in the wireless medium. The radio includes anover-voltage or over-power detector that has an OVD thresholdapproximately at the −40 dBm level (threshold between the second story303 and the third story 305) when the baseband amplifiers are set to apredetermined maximum level of approximately 40 dB. At this level, theADCs have a maximum level or window set approximately at the −64 dBmlevel (threshold between the first story 301 and the second story 303).In this manner, a packet having a very strong power level exceeding theOVD threshold and causing an OVD signal indicates that the power rangeof the signal is within the third story 305. A signal that does notexceed the OVD threshold but that causes clipping of the ADCs indicatesthat the power range of the signal is within the second story 303. Anincrease in the power level by a predetermined amount above the trackednoise floor level, such as a power rise of between 4–6 dB, but that doesnot cause clipping of the ADCs indicates a relatively weak signal withinthe first story 301.

It is appreciated that operation in the first story 301 is unique tooperation in the other two stories 303 and 305. The ADC back-off for thefirst story 301 is relatively large and provides power visibility overthe entire power range of the first story 301. The signal power back-offinto the ADCs can be as large as 30 dB with reliable reception. Thisprovides a rather large power aperture for fast antenna diversityscanning. As previously described, for OFDM-type packets, the normaltime budget allows only up to about 5–6 μs of preamble for AGC andantenna diversity. Furthermore, ZIF-based AGC/DC algorithms must contendwith changing DC versus gain. The relatively high resolution ADCs helpto mitigate the DC issue. High resolution ADCs provide wide signal gainaperture for weak to strong signals. The high resolution of the ADCs isexploited allowing limiting the maximum baseband amplifier gain (e.g.,max of 40 dB) and utilizing a large signal back-off for weak signals.Limited gain reduces the DC budget with which the AGC functions mustcontend. The high resolution of the ADCs results in a relatively broadvisibility of the AGC, so that the AGC can instantaneously see signalsover a larger dynamic range.

In particular, the large visibility of the ADCs enable instantaneouspower observations over a power range of up to 30 dB above the −92 dBmnoise floor, or up to approximately −62 dBm. It has been determined thatthis is the beneficial region for power-based hardware diversity. Thespectral limit for receiver sensitivity of a 54 megabit per second(Mbps) signal is −65 dBm. Signals with greater power levels operativewithin the second or third stories 303, 305 are detected and acquiredwith either antenna so that diversity is less of an issue. At the weakerpower levels of the first story 301, however, antenna selection is mostbeneficial.

FIG. 4 is a figurative diagram of an exemplary timeline illustratingantenna measurement and selection within the SS section 201 of anincoming packet for two antennas 1 and 2. Each block represents an 800ns timing interval. The timeline is initiated at a first block 1indicating a power level measure trip in which the transceiver 100detected a rise in the power level relative to the measured noise floorby the threshold amount. In an exemplary embodiment, for example, thethreshold power level differential is approximately 4–6 dB indicative ofthe presence of a packet, so that any rise in power level above thethreshold initiates AGC and antenna diversity selection. It is noted,however, that if the signal power level is significant enough to causeclipping of the ADCs and/or the OVD condition, that the antennadiversity functions may be considered unnecessary.

At next block 2, the transceiver 100 measures the power level using afirst antenna 1 assuming a power level range between approximately −92to −62 dBm. At next block 3, the transceiver 100 switches to antenna 2,switches DC compensation level for antenna 2, and allows any transientsto settle. At next block 4, the transceiver 100 measures the power levelusing antenna 2. At next block 5, the transceiver 100 selects theantenna having the higher power level, switches the antenna and DCcompensation, if necessary, and allows transient settling. At next block6, the transceiver 100 measures the power level and the DC level usingthe selected antenna for fine gain and DC adjustments. At next block 7,the transceiver 100 performs fine gain and DC adjustments based onmeasured power and DC levels, and allows transients to settle. In oneembodiment, for example, the gain of a digital feed-forward gainamplifier (not shown) is determined for fine gain adjust. The equivalentduration for hardware diversity selection is 5.6 μs corresponding to 7short syncs, which is within the allocated time budget.

FIG. 5 is a figurative diagram of an exemplary timeline illustratingantenna measurement and selection within the SS section 201 of anincoming packet for 3 antennas. The power measure trip occurs in block 1and a power measurement is taken using antenna 1 in block 2. In block 3,the transceiver 100 switches to antenna 2 and switches DC compensationlevel appropriate for antenna 2 and allows transients to settle. At nextblock 4, a power level measurement is taken using antenna 2. At nextblock 5, the transceiver 100 switches to antenna 3 and switches DCcompensation level appropriate for antenna 3 and allows transients tosettle. At next block 6, a power level measurement is taken usingantenna 3. At next block 7, the transceiver 100 selects the antenna withthe highest power level, switches the antenna and corresponding DCcompensation level, if necessary, and allows transient settling. At nextblock 8, the power and DC levels are measured using the selectedantenna. At next block 9, the transceiver 100 performs fine adjust andsettling as previously described. The equivalent duration for hardwarediversity selection in this case is approximately 7.2 μs correspondingto 9 short syncs. In this case, the time budget of the acquisitionprocess is modified to a maximum time budget range of about 10 shortsyncs or about 8 μs.

As described above, utilizing the full capability of the ADC to providelarge signal back-offs provides increased visibility. An alternativemethod for increased visibility is to stack the ADCs to effectivelydouble the cumulative visibility of the AGC. At baseband, there are twoADCs including an I-channel ADC and a Q-channel ADC. In this case, oneof the ADCs, such as the I-channel ADC, is set at a gain level tomonitor the first story 301 of the dynamic power range. The other ADC isset at a different gain level to monitor the second story 303 dynamicrange.

The fundamental issues when switching antennas include transientsinduced by antenna switching, DC changes due to new signal path, andgain changes due to new signal path. A few issues that enable success ofpower-based, hardware diversity for OFDM WLANs with ZIF include theability of the baseband AGC to see the dynamic range of interest inminimal time, the elimination of DC in minimum time, mitigationtechniques for DC changes with antenna switching, and mitigationtechniques for gain changes with antenna switching. In anotherembodiment, the AGC time budget is re-allocated to provide more timeand/or to enable diversity among 3 or more antennas.

It is noted that DC elimination is important to maintaining signalvisibility at baseband in ZIF implementations. DC budgets indicate thatDC could change significantly as a result of antenna switching. Asignificant amount of unexpected DC can saturate the ADC regardless ofthe actual power level of the signal, which would otherwise require timeto track out and resolve. There may not be enough time for hardwarediversity to resolve unexpected DC. In one embodiment, the amount of DCcorrection is predetermined and known at the time of antenna switching.In this case, the transceiver 100 is able to switch the antenna whileimmediately applying a new, predetermined DC correction term. The DCDACs (not shown) are essentially instantaneous and thus allow forinstantaneous changes in DC correction without significant delays. Inone embodiment, relatively large DC DACs (e.g., 12-bit DACs) areemployed to handle a wide range of DC offsets. Settling through theradio is very quick. If a high-pass filter (HPF) is employed, however,the bandwidth-dependent settling time must be accounted for during eachswitch, so that settling time may consume too much time.

A first approach for DC compensation is calibration at time ofmanufacture to determine the DC levels for each antenna path. Thismethod suffers, however, over time from errors due to factors such asdrift, aging, heat, etc. Alternatively, an antenna DC table isdynamically maintained during radio operation storing a DC value foreach antenna. Alternating between the antennas allowsmaintenance/updating of the measured DC values stored in the antenna DCtable. In one embodiment, the DC values are measured during noisetracking while receiving noise level in the absence of a packet. The DCthrough one of the antennas is measured while tracking noise, and thetransceiver 100 switches to the other antenna while idle to determinethe DC on the other path. The rate at which the antennas are visited isbased on expected DC versus time characteristic.

In a more specific embodiment, the DC per antenna is determined atend-of-packet (EOP) (e.g., just after completion of a packettransmission in the wireless medium). At EOP, the AGC performsstepped-gain descent to acquire the noise floor to determine DC. At thisgain level, the EOP alternates between the antennas to determine the DClevel for each antenna. The measured DC values are stored in the antennaDC table. The stored DC values are used by the hardware to correct DCinstantaneously when switching antennas during packet onset.

Gain variations associated with antenna switching are more stable.Antenna switches typically have different loss characteristics betweensignal paths, which are relatively stable over time. Measurement at timeof manufacture provides calibration data for antenna power measures,which may be stored (e.g., in a look-up table) and used during gainswitching. In an alternative embodiment, the gain and/or noise floordifference between the antennas is measured for each antenna. Forexample, the noise floor is measured for each antenna and thecorresponding gain values are used to determine the relative gaindifferences based on measured noise floor differences. In oneembodiment, for example, the gain per antenna is maintained byalternating between antennas while receiving noise. In a more particularembodiment, the gain per antenna is maintained by alternating betweenantennas and measuring gain after EOP.

Normally, the AGC and diversity functions are allotted approximately 5.6μs from the onset of a packet. The final 2.4 μs is allocated to CFOacquisition, which relieves the processing required for LS processing.The long sync time estimation and the FFO estimation each only have tohandle approximately +/−156 kilohertz (kHz). In an alternativeembodiment, the AGC is allocated the full 8 μs of the SS section 201 ifthe long sync processing instead handles an offset of approximately+/−276 kHz. In particular, the long sync correlator is modified to abank of correlators, such as, for example, at least two correlators. Inthe two correlator configuration, each is tuned to a different frequencyoffset, such as, for example, +120 kHz and −120 kHz, and each handles anoffset range of approximately +/−156 kHz. In this manner, eachcorrelator handles an offset range of +/−156 kHz relative to itsfrequency offset position (+120 kHz or −120 kHz), for a combinationfrequency range of approximately +/−276 kHz. The outputs of the twooffset correlators are used to determine the frequency offset within+/−276 kHz. For example, the outputs are combined to interpolate orotherwise extrapolate the CFO estimation within the +/−276 kHz range.The CFO estimation may be performed at the beginning of the LS section203 including overlapping the GI2 guard interval. The FFO estimationoperates as normal and can be completed within the remaining time of theLS section 203.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions andvariations are possible and contemplated. Those skilled in the artshould appreciate that they can readily use the disclosed conception andspecific embodiments as a basis for designing or modifying otherstructures for providing out the same purposes of the present inventionwithout departing from the spirit and scope of the invention.

1. A power-based hardware antenna diversity method for a wirelesstransceiver with multiple antennas, comprising: setting gain at amaximum level to establish a first story of dynamic power range above anoise floor level; using a high-resolution ADC at a large back-off levelrelative to the noise floor to detect weak signals within the firststory of the dynamic power range; switching antennas and measuring powerlevel for each antenna during signal onset; and selecting an antennahaving a largest power level.
 2. The power-based hardware antennadiversity method of claim 1, further comprising: measuring a DCcharacteristic for each antenna; storing each measured DCcharacteristic; and applying a corresponding DC characteristic duringsaid step of switching antennas and measuring power level for eachantenna.
 3. The power-based hardware antenna diversity method of claim2, wherein said measuring comprises measuring at EOP.
 4. The power-basedhardware antenna diversity method of claim 1, further comprisingmeasuring gain characteristics of each antenna and storing correspondinggain mitigation values.
 5. The power-based hardware antenna diversitymethod of claim 1, further comprising measuring relative noise floorgain differences between each antenna and storing corresponding gainmitigation values.
 6. The power-based hardware antenna diversity methodof claim 1, further comprising employing at least two long synccorrelators for performing course frequency offset estimation at thebeginning of a long sync section of an incoming packet.
 7. A method forperforming hardware diversity based on power in a wireless transceiverhaving multiple antennas, comprising: setting a transceiver gain at amaximum level to establish a first story of dynamic power range above anoise floor level; using a high-resolution ADC at a large back-off levelrelative to the noise floor to detect weak signals within the firststory of the dynamic power range; switching antennas and measuring powerlevel for each antenna during signal onset; and selecting an antennahaving a largest measured power level.
 8. The method of claim 7, furthercomprising: measuring a DC characteristic for each antenna; storing eachmeasured DC characteristic in a memory; and for each antenna, applying acorresponding DC characteristic during said step of measuring the powerlevel.
 9. The method of claim 7, wherein said measuring comprisesmeasuring at EOP.
 10. The method of claim 7, further comprisingmeasuring gain characteristics of each antenna and storing correspondinggain mitigation values in a memory.
 11. The method of claim 7, furthercomprising measuring relative noise floor gain differences between eachantenna and storing corresponding gain mitigation values in a memory.12. The method of claim 7, further comprising employing at least twolong sync correlators for performing course frequency offset estimationat the beginning of a long sync section of an incoming packet.